A voltage controlled oscillator (VCO) or oscillator is a component that can be used to translate DC power into a radio frequency (RF) signal. In general, VCOs are designed to produce an oscillating signal of a particular frequency corresponding to a given tuning voltage. The frequency of the oscillating signal is dependent upon the magnitude of a tuning voltage. A high frequency signal can be generated either by an oscillator operating at a fundamental frequency or a harmonic oscillator. An oscillator operating at the fundamental frequency typically suffers from a low Q-factor, insufficient device gain and higher phase noise at a high frequency of operation. In contrast, harmonic oscillators may be operated at a lower frequency, and generally include a high Q-factor, high device gain and low phase noise. A frequency doubler and other means of up-conversion may provide a practical and quick solution to generate a high frequency signal from an oscillator operating at a lower frequency, however, they may also introduce distortions and provide poor phase noise performance.
It is very difficult to design a high frequency signal source with good phase noise for millimeter wave applications. Conventional implementations employ multipliers and buffer/power amplifiers to multiply the fundamental frequency of a voltage controlled oscillator (VCO) to millimeter wave bands (e.g., greater than 50 GHz). These conventional implementations have several problems. For example, the employment of the several multipliers and buffer/power amplifiers add to the complexity of the topology in addition to adding to the phase noise degradation. Additionally, the performance of the high frequency source signal is parasitic sensitive, such that the parasitics of each buffer/amplifier stage further degrade the performance of the high frequency source signal. The employment of several multipliers and buffer/power amplifiers results in high power consumption, tedious and challenging tuning work associated with one or more tuning resonators in addition to high overall costs.